The following Non-Patent Literature 1 discloses a transceiver for transmitting and receiving a high frequency signal.
This transceiver includes a transmission baseband unit, a quadrature modulator, a quadrature demodulator, and a reception baseband unit.
The quadrature modulator includes a transmission local signal generating unit, and the quadrature demodulator includes a reception local signal generating unit.
The transmission local signal generating unit generates a transmission local signal having the same frequency as a carrier frequency.
The reception local signal generating unit generates a reception local signal having a different frequency from the transmission local signal.
The quadrature modulator includes a 90° phase difference generating unit for outputting a first transmission local signal having the same frequency as the transmission local signal generated by the transmission local signal generating unit from a terminal, a, and outputting a second transmission local signal having a phase ahead of the first transmission local signal by 90° from a terminal, b.
Using the first transmission local signal generated by the 90° phase difference generating unit, the quadrature modulator converts the frequency of a transmission I-phase signal (hereinafter referred to as “TXI signal”) of a transmission baseband signal output from the transmission baseband unit.
In addition, using the second transmission local signal generated by the 90° phase difference generating unit, the quadrature modulator converts the frequency of a transmission Q-phase signal (hereinafter referred to as “TXQ signal”) of the transmission baseband signal.
Then, the quadrature modulator synthesizes the frequency-converted transmission I-phase signal with the frequency-converted transmission Q-phase signal, and outputs a high frequency signal (hereinafter referred to as “TXO signal”) which is a synthesized signal thereof.
However, when there is a difference between a frequency characteristic of a path through which the TXI signal is transmitted from the transmission baseband unit to the quadrature modulator and a frequency characteristic of a path through which the TXQ signal is transmitted from the transmission baseband unit to the quadrature modulator, an image component may be generated in the TXO signal, and a communication characteristic of the TXO signal may be deteriorated. The frequency characteristic of a path corresponds to a passing loss in the path, a passing phase in the path, or the like.
The transceiver disclosed in Non-Patent Literature 1 has a function of correcting a difference between a frequency characteristic of a path through which the TXI signal is transmitted and a frequency characteristic of a path through which the TXQ signal is transmitted.
The transceiver disclosed in Non-Patent Literature 1 corrects the difference between the frequency characteristic of a path through which the TXI signal is transmitted and the frequency characteristic of a path through which the TXQ signal is transmitted in the following manner.
The quadrature demodulator of the transceiver includes the 90° phase difference generating unit for outputting a first reception local signal having the same frequency as the reception local signal generated by the reception local signal generating unit from a terminal a and outputting a second reception local signal having a phase ahead of the first reception local signal by 90° from a terminal b.
Using the first reception local signal generated by the 90° phase difference generating unit, the quadrature demodulator converts the frequency of the TXO signal output from the quadrature modulator and outputs the frequency-converted TXO signal as a reception I-phase signal (hereinafter referred to as “RXI signal”).
In addition, using the second reception local signal generated by the 90° phase difference generating unit, the quadrature demodulator converts the frequency of the TXO signal output from the quadrature modulator and outputs the frequency-converted TXO signal as a reception Q-phase signal (hereinafter referred to as “RXQ signal”).
The reception baseband unit of the transceiver measures the RXI signal and the RXQ signal output from the quadrature demodulator.
The transmission baseband unit of the transceiver calculates a difference between a frequency characteristic of a path through which a TXI signal is transmitted and a frequency characteristic of a path through which a TXQ signal is transmitted, from the RXI signal and the RXQ signal measured by the reception baseband unit.
The frequency of a reception local signal generated by the reception local signal generating unit is offset with respect to a transmission local signal generated by the transmission local signal generating unit, and therefore the transmission baseband unit can calculate a difference between the frequency characteristics of the two paths.
The transmission baseband unit corrects the difference between the frequency characteristics of the paths on the basis of the calculation result of the difference between the frequency characteristics of the two paths.